1. Field of the Invention
The present invention relates to a method and apparatus for detecting microparticles in fluid samples. More particularly, the present invention relates to a method and apparatus which uses a fluid delivery system and laser fluorescence detection system to detect fluorescently tagged microparticles in low concentrations in fluid samples.
2. Description of Related Art
Detection of microorganisms present at low concentration in fluids is critical to provide microbiological contamination answers faster to better treat patient diseases, to prevent deadly outbreaks, to better manage quality control processes in food, drink, and drug manufacturing plants, and to provide scientists with powerful and easy to use analytical research tools.
Testing methods for microorganisms such as M. tuberculosis, Trichomonas vaginalis, Campylobacter, Salmonella, E. coli, and Cyclospora include growth culture methods, PCR methods, fluorescently enhanced microscopic visualizations, ATP bioluminescence techniques, and bactometers. These methods are often slow and expensive, and have limited detection capabilities.
Testing devices include epifluorescent microscopes, fluorometers, and flow cytometers. Epifluorescent microscopes are coupled with cooled CCD high-resolution cameras to permit epifluorescent microscopic visualizations of microscopic particles. Fluorometers have limited detection capabilities, and is also not well suited when spectral differentiation in a large population of organisms is required. This is often the case when live versus dead organism differentiation is required. Flow cytometers can be very accurate in detecting and differentiating immuno-fluorescently dead or live labeled particles. However, flow cytometers are expensive and require an experienced technician or scientist to operate it and interpret the data.
Cryptosporidium oocysts and Giardia cysts may be detected using an immunofluorescent assay (IFA) procedure. This method uses polyclonal antibodies to stain the cysts which then can be detected by epifluorescent microscopy. This method is extremely labor-intensive, considering the number of particles to be investigated under the epifluorescent microscope by an experienced technician. Flow cytometeters may also be used, but they are very expensive and require an experienced and well-trained technician to operate. Furthermore, flow cytometers still require microscopy confirmation of oocyst identification.
Water quality monitoring is vital for managing supplies of unpolluted water for agriculture, industry, and human consumption. Water quality monitoring may be performed using test organisms as indicators of freshwater toxicity, for example, the fathead minnow Pimephales promelas, the cladoceran Ceriodaphnia dubia, and the green alga Selenastrum capricornutum. Test organisms are cultured under standard conditions, and exposed for a period of time to toxicants. Comparison of survival and reproduction rates of test organisms to control organisms provides an indication of water toxicity.
Bacteria enzyme activity may be used to assess water quality by using a specially designed enzyme substrate that becomes fluorescent when cleaved. This substrate is cleaved by enzymes in the bacteria and emits fluorescence light when exposed to light of the proper wavelength. The rate of enzyme activity can be measured using a fluorometer, and provides an indirect measurement of the level of toxicant stress on the bacteria.
Zooplankton feeding behavior may also be used to assess water quality. Extensive acute toxicity studies have been performed using plankton, in general, and various species of rotifer, in particular. Rotifer feeding and reproduction rates can be used as a rapid toxicity assessment tool. The effect of a wide range of chemicals including xylene, cadmium, copper, mercury, and diazanon on the feeding and reproduction rates of the rotifer Brachionus calyciflorus for fresh water and Brachionus plicatilis for marine waters has been extensively studied. In the feeding rate method, the rotifers are exposed for several minutes to water containing a toxicant, and then allowed to feed on fluorescently labeled beads. The rotifers are then anesthetized, washed, transferred to a microscope slide, and individually examined using a fluorescent microscope. The feeding rate is estimated by quantifying the intensity of fluorescence of ingested beads in the digestive tract of individual rotifers using an imaging technique. This method requires a trained operator, a camera, and a fluorescent microscope, which makes it slow and expensive.
What is needed are methods and apparatus for detecting microparticles such as harmful microorganisms and assessing water quality which is rapid, sensitive, reproducible, substantially automatic, and cost-effective.
The present invention is a device for detecting a fluorescent substance tagged to a microparticle. The device comprises a single capillary flow carrier system for transporting the microparticle past a selected location, a source of electromagnetic radiation for irradiating the substance tagged to the microparticle, and a detection system for measuring fluorescent light emitted from the substance at the selected location.